An object conforming to the MGLOfflineRegion protocol determines which
resources are required by an MGLOfflinePack object. At present, only
instances of MGLTilePyramidOfflineRegion may be used as MGLOfflinePack
regions, but additional conforming implementations may be added in the future.

Declaration

MGLOfflineStorage implements a singleton (shared object) that manages offline
packs. All of this class’s instance methods are asynchronous, reflecting the
fact that offline resources are stored in a database. The shared object
maintains a canonical collection of offline packs in its packs property.